1. Field of the Invention
The invention is directed to a self-pumping hydropneumatic spring leg or suspension strut with internal level or ride-height control, particularly for motor vehicles, with an outer tube with an oil-filled high-pressure work space in the work cylinder under the pressure of at least one gas cushion acting as spring in a high-pressure chamber, a second work space on the piston rod side, and an axially displaceable piston which is supported by a hollow piston rod and is sealed in the work cylinder. The piston rod which is driven by the springing movement of the vehicle, conveys oil from a low-pressure chamber to the work space connected to the high-pressure chamber and comprises a pump rod and a pump cylinder formed by the hollow piston rod.
2. Description of the Related Art
Self-pumping hydropneumatic suspension struts with internal ride-height control are already known (e.g., DE 196 48 859 C2), wherein the suspension strut must usually travel a substantially shorter path than the vehicle wheel due to the articulation in the vehicle. This results in a short construction with a large outer diameter.
U.S. Pat. No. 5,797,594 discloses a suspension strut in which no separation is provided in the high-pressure space between the oil and the high-pressure gas, so that the changes in spring gas volume caused by pressure and temperature lead to unacceptable changes in spring force.
Further, pressure vessels for enclosing a gas mass are known (e.g., DE 198 35 222 A1) in which the gas mass enclosed by an oil body which changes in shape is pretensioned. The wall of the enveloping body is formed at least partially from a gastight barrier layer and the wall is constructed in multiple layers.
In one direction of development taken in automotive engineering, the wheel path is in a ratio of about 1:1 to the path of the suspension strut. This means that suspension struts are provided which have small diameters, but have a corresponding length. Suspension struts with small diameters are required whenever it is desirable to have a reasonable width of the back loading space for the trunk of a vehicle.
According to the suspension strut (e.g., DE 196 48 859 C2), the device cannot be lengthened to any extent desired and the diameter can not be reduced to any extent desired because this would require a diaphragm or membrane for separating the high-pressure gas in a correspondingly long construction. Since the elastic membrane allows corresponding gas diffusion over the course of its service life, an overlong membrane would accelerate this gas diffusion. Further, there is no conducting of heat from the oil at the outer tube of the suspension strut because the gas between the outer tube and work cylinder brings about an insulating effect.
It is the object of the invention to provide a self-pumping hydropneumatic suspension strut with internal ride-height control in which smaller outer diameters can be produced with a correspondingly greater length of the suspension strut. In this regard, not only can a sufficient volume of gas be received in the high-pressure chamber, but adequate cooling of the oil can also be retained.
According to the invention, this object is met in that the high-pressure chamber is connected with a flow connection arranged in the piston rod guide, wherein a first filling bore hole arranged in the outer tube communicates with the flow connection when the piston rod guide is not completely assembled, and in that the filling bore hole is closed by the piston rod guide after the piston rod guide slides axially into the outer tube. In this regard, it is advantageous that the necessary internal parts, e.g., the high-pressure chamber, the piston, the piston rod and the pump rod, together with the piston rod guide, are introduced axially into the outer tube of the suspension strut and that the suspension strut is operational after filling at least the high-pressure chamber with pressure gas via the filling bore hole, and that after the piston rod guide is slid in farther axially together with the work cylinder and the rest of the internal parts the filling bore hole is closed by the piston rod guide, so that the suspension strut is completely assembled after the outer tube has been flanged.
In order to achieve adequate cooling of the oil, it is provided according to another feature that an enveloping body which changes in shape and whose wall comprises a gastight barrier layer is provided as high-pressure chamber. The advantage in this regard consists in that the high-pressure chamber in the form of an enveloping body can be arranged concentrically between the outer tube and the work cylinder and the oil in the suspension strut can reach the area of the inner wall of the outer tube in order to give off its heat to the atmosphere via the outer tube.
According to another essential feature, the enveloping body has a connection element which is received in an opening of the flow connection. It is advantageous that the high-pressure chamber in the form of the enveloping body is received in the opening of the flow connection in the manner of a plug-in connection. There is a frictional engagement and/or positive engagement between the connection element of the enveloping body and the piston rod guide.
According to another construction, the enveloping body is provided in the area of a connection element with a check valve. The advantage in this regard consists in that the pressure gas introduced into the enveloping body can not readily escape again.
According to another feature, the low-pressure chamber communicates with a second filling bore hole arranged in the outer tube when the intermediate base or piston rod guide is not completely mounted and, after the intermediate base or piston rod guide slides axially into the outer tube, the second filling bore hole is closed by the intermediate base or the piston rod guide.
Faultless sealing is ensured in that the piston rod guide or the intermediate base has a seal in the area adjoining the filling bore hole.
According to another essential feature, the high-pressure chamber arranged between the work cylinder and the outer tube is surrounded by oil.
It is ensured that the internal parts which are joined together as a constructional unit are fixed in a simple manner with respect to manufacturing in that the outer tube is provided for supporting an intermediate base with partial indentations which are arranged from the radial outer side to the radial inner side or in that the outer tube is provided with a circumferentially extending flange or bead which is pressed in radially, an intermediate base contacting the bead in the interior of the outer tube.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.